diff --git a/README.md b/README.md
index a4e0b16..5423157 100644
--- a/README.md
+++ b/README.md
@@ -103,9 +103,9 @@ section of nginx configuration.
     metric names on output.
   * `error_metric_name` (string): Can be used to change the default name of
     error metric (see [Built-in metrics](#built-in-metrics) for details).
-  * `sync_interval` (number): sets per-worker counter sync interval in seconds.
-    This sets the boundary on eventual consistency of counter metrics. Defaults
-    to 1.
+  * `sync_interval` (number): sets the sync interval for per-worker counters and
+    key index (in seconds). This sets the boundary on eventual consistency of
+    counter metric increments, and metric resets/deletions. Defaults to 1.
   * `lookup_max_size` (number): maximum size of a per-metric lookup table
     maintained by each worker to cache full metric names. Defaults to 1000.
     If you have metrics with extremely high cardinality and lots of available
diff --git a/prometheus.lua b/prometheus.lua
index 2ff3aa8..02ad1a4 100644
--- a/prometheus.lua
+++ b/prometheus.lua
@@ -111,7 +111,7 @@ local ERR_MSG_COUNTER_NOT_INITIALIZED = "counter not initialized! " ..
 -- Error message that gets logged when the shared dictionary gets full.
 local ERR_MSG_LRU_EVICTION = "Shared dictionary used for prometheus metrics " ..
   "is full. REPORTED METRIC DATA MIGHT BE INCOMPLETE. Please increase the " ..
-  "size of the dictionary or decrease metric cardinality."
+  "size of the dictionary or reduce metric cardinality."
 
 -- Accepted range of byte values for tailing bytes of utf8 strings.
 -- This is defined outside of the validate_utf8_string function as a const
@@ -384,8 +384,7 @@ local function lookup_or_create(self, label_values)
   end
 
   if self.lookup_size >= self.lookup_max_size then
-    self.lookup_size = 0
-    self.lookup = {}
+    self:reset_lookup()
   end
 
   local t = self.lookup
@@ -547,6 +546,9 @@ local function del(self, label_values)
   if err then
     self._log_error("Error deleting key: ".. k .. ": " .. err)
   end
+
+  -- Clean up the full metric name lookup table as well.
+  self.lookup = {}
 end
 
 -- Set the value of a gauge metric.
@@ -623,6 +625,12 @@ local function observe(self, value, label_values)
   end
 end
 
+-- Reset the metric name lookup table for a given metric.
+local function reset_lookup(self)
+  self.lookup_size = 0
+  self.lookup = {}
+end
+
 -- Delete all metrics for a given gauge, counter or a histogram.
 --
 -- This is like `del`, but will delete all time series for all previously
@@ -691,7 +699,7 @@ local function reset(self)
   end
 
   -- Clean up the full metric name lookup table as well.
-  self.lookup = {}
+  self:reset_lookup()
 end
 
 -- Initialize the module.
@@ -738,7 +746,22 @@ function Prometheus.init(dict_name, options_or_prefix)
   end
 
   self.registry = {}
-  self.key_index = key_index_lib.new(self.dict, KEY_INDEX_PREFIX)
+  self.key_index = key_index_lib.new(self.dict, KEY_INDEX_PREFIX, function(metric_key)
+    -- When another worker calls reset or del on a metric, reset that
+    -- metric's local lookup table.
+    local metric_name = ngx_re_gsub(metric_key, "{.*", "", "jo")
+    if self.registry[metric_name] then
+      local m = self.registry[metric_name]
+      m.lookup = {}
+      return
+    end
+
+    metric_name = ngx_re_gsub(metric_name, "_sum$", "", "jo")
+    local m = self.registry[metric_name]
+    if m and m.typ == TYPE_HISTOGRAM then
+      m:reset_lookup()
+    end
+  end)
 
   self.initialized = true
 
@@ -757,7 +780,7 @@ end
 
 -- Initialize the worker counter.
 --
--- This can call this function from the `init_worker_by_lua` if you are calling
+-- You can call this function from the `init_worker_by_lua` if you are calling
 -- Prometheus.init() from `init_by_lua`, but this is deprecated. Instead, just
 -- call Prometheus.init() from `init_worker_by_lua_block` and pass sync_interval
 -- as part of the `options` argument if you need.
@@ -782,6 +805,10 @@ function Prometheus:init_worker(sync_interval)
     error(err, 2)
   end
   self._counter = counter_instance
+
+  ngx.timer.every(self.sync_interval, function (_)
+    self.key_index:sync()
+  end)
 end
 
 -- Register a new metric.
@@ -844,6 +871,7 @@ local function register(self, name, help, label_names, buckets, typ)
     lookup = {},
     lookup_size = 0,
     lookup_max_size = self.lookup_max_size,
+    reset_lookup = reset_lookup,
     parent = self,
     -- Store a reference for logging functions for faster lookup.
     _log_error = function(...) self:log_error(...) end,
diff --git a/prometheus_keys.lua b/prometheus_keys.lua
index cc763a9..9013652 100644
--- a/prometheus_keys.lua
+++ b/prometheus_keys.lua
@@ -8,7 +8,7 @@
 local KeyIndex = {}
 KeyIndex.__index = KeyIndex
 
-function KeyIndex.new(shared_dict, prefix)
+function KeyIndex.new(shared_dict, prefix, delete_callback)
   local self = setmetatable({}, KeyIndex)
   self.dict = shared_dict
   self.key_prefix = prefix .. "key_"
@@ -18,6 +18,7 @@ function KeyIndex.new(shared_dict, prefix)
   self.deleted = 0
   self.keys = {}
   self.index = {}
+  self.delete_callback = delete_callback
   return self
 end
 
@@ -45,6 +46,7 @@ function KeyIndex:sync_range(first, last)
       self.keys[i] = key
       self.index[key] = i
     elseif self.keys[i] then
+      self.delete_callback(self.keys[i])
       self.index[self.keys[i]] = nil
       self.keys[i] = nil
     end
@@ -114,7 +116,7 @@ function KeyIndex:remove(key, err_msg_lru_eviction)
     self.dict:set(self.key_prefix .. i, nil)
     self.deleted = self.deleted + 1
 
-    -- increment delete_count to signalize other workers that they should do a full sync
+    -- increment delete_count to signal other workers that they should do a full sync
     local _, err, forcible = self.dict:incr(self.delete_count, 1, 0)
     if err or forcible then
       return err or err_msg_lru_eviction
diff --git a/prometheus_test.lua b/prometheus_test.lua
index d0b4f8e..ba98b1b 100644
--- a/prometheus_test.lua
+++ b/prometheus_test.lua
@@ -104,13 +104,18 @@ function TestPrometheus:setUp()
   self.dict = setmetatable({}, SimpleDict)
   ngx.shared.metrics = self.dict
   self.p = require('prometheus').init('metrics')
+  -- Another instance of the library to simulate a second nginx worker.
+  self.p2 = require('prometheus').init('metrics')
   self.counter1 = self.p:counter("metric1", "Metric 1")
   self.counter2 = self.p:counter("metric2", "Metric 2", {"f2", "f1"})
   self.counter3 = self.p:counter("metric3", "Metric 3", {"f3"})
   self.counter4 = self.p:counter("metric4", "Metric 4", {"f1","f2","f3"})
   self.gauge1 = self.p:gauge("gauge1", "Gauge 1")
+  self.gauge1_p2 = self.p2:gauge("gauge1", "Gauge 1")
   self.gauge2 = self.p:gauge("gauge2", "Gauge 2", {"f2", "f1"})
+  self.gauge2_p2 = self.p2:gauge("gauge2", "Gauge 2", {"f2", "f1"})
   self.hist1 = self.p:histogram("l1", "Histogram 1")
+  self.hist1_p2 = self.p2:histogram("l1", "Histogram 1")
   self.hist2 = self.p:histogram("l2", "Histogram 2", {"var", "site"})
 end
 function TestPrometheus.tearDown()
@@ -411,6 +416,7 @@ function TestPrometheus:testReset()
   self.gauge1:reset()
   self.p.key_index:sync()
   luaunit.assertEquals(self.dict:get("gauge1"), nil)
+  luaunit.assertEquals(self.gauge1.lookup, {})
   luaunit.assertEquals(self.dict:get("nginx_metric_errors_total"), 0)
 
   self.gauge1:inc(3)
@@ -522,6 +528,43 @@ function TestPrometheus:testReset()
   luaunit.assertEquals(self.dict:get('l2_sum{var="ok",site="site1"}'), nil)
   luaunit.assertEquals(self.dict:get("nginx_metric_errors_total"), 0)
 
+  -- Set a gauge value that will be reset by another worker.
+  self.gauge1:set(42)
+  self.gauge2:set(91, {"a", "b1"})
+  self.gauge2:set(92, {"a", "b2"})
+  luaunit.assertEquals(self.dict:get("gauge1"), 42)
+  luaunit.assertEquals(self.dict:get('gauge2{f2="a",f1="b1"}'), 91)
+  luaunit.assertEquals(self.dict:get('gauge2{f2="a",f1="b2"}'), 92)
+  luaunit.assertNotEquals(self.gauge1.lookup, {})
+  luaunit.assertNotEquals(self.gauge2.lookup, {})
+  luaunit.assertEquals(self.dict:get("nginx_metric_errors_total"), 0)
+
+  -- After another worker has reset the metric, confirm that the per-metric
+  -- lookup table has been reset.
+  self.gauge1_p2:reset()
+  self.gauge2_p2:del({"a", "b1"})
+  self.p.key_index:sync()
+  luaunit.assertEquals(self.dict:get("gauge1"), nil)
+  luaunit.assertEquals(self.dict:get('gauge2{f2="a",f1="b1"}'), nil)
+  luaunit.assertEquals(self.dict:get('gauge2{f2="a",f1="b2"}'), 92)
+  luaunit.assertEquals(self.gauge1.lookup, {})
+  luaunit.assertEquals(self.gauge2.lookup, {})
+  luaunit.assertEquals(self.dict:get("nginx_metric_errors_total"), 0)
+
+  -- Similarly, check that a histogram metric reset by another worker
+  -- results in metric lookup table being reset.
+  self.hist1:reset()
+  self.hist1:observe(0.44)
+  self.p._counter:sync()
+  luaunit.assertEquals(self.dict:get('l1_sum'), 0.44)
+  luaunit.assertNotEquals(self.hist1.lookup, {})
+
+  self.hist1_p2:reset()
+  self.p.key_index:sync()
+  luaunit.assertEquals(self.dict:get('l1_sum'), nil)
+  luaunit.assertEquals(self.hist1.lookup, {})
+  luaunit.assertEquals(self.hist1_p2.lookup, {})
+
   -- key not exist
   self.gauge2:inc(4, {"key_not_exist", "key_not_exist"})
   self.gauge2:reset()
@@ -705,7 +748,9 @@ TestKeyIndex = {}
 function TestKeyIndex:setUp()
   self.dict = setmetatable({}, SimpleDict)
   ngx.shared.metrics = self.dict
-  self.key_index = require('prometheus_keys').new(self.dict, '_prefix_')
+  self.key_index = require('prometheus_keys').new(self.dict, '_prefix_', function(key)
+    self.last_deleted_key = key
+  end)
 end
 function TestKeyIndex.tearDown()
   ngx.logs = nil
@@ -795,13 +840,13 @@ function TestKeyIndex:testSync()
   -- key deleted by another worker
   self.dict:set("_prefix_delete_count", 1)
   self.dict:delete("_prefix_key_2")
-  self.dict:set("_prefix_key_3", "key3")
   self.key_index:sync()
   keys = self.key_index:list()
   luaunit.assertEquals(ngx.logs, nil)
   luaunit.assertEquals(#keys, 2)
   luaunit.assertEquals(keys[1], "key1")
   luaunit.assertEquals(keys[2], "key3")
+  luaunit.assertEquals(self.last_deleted_key, "key2")
 end
 
 function TestPrometheus:testLookupMaxSize()