diff --git a/Changes.md b/Changes.md
index df78c107e21..aabdf43abd7 100644
--- a/Changes.md
+++ b/Changes.md
@@ -92,7 +92,9 @@ API
 - OpenColorIOAlgo : Added a new namespace that allows the OpenColorIO config and working space to be defined via the Gaffer context.
 - OpenColorIOConfigPlug : Added a new plug type to aid in configuring the OpenColorIO context for a ScriptNode.
 - ImageReader/ImageWriter : Added a `config` argument to the `DefaultColorSpaceFunction` definition. This is passed the OpenColorIO config currently being used by the node.
-- ValuePlugs : Added Python bindings for `ValueType` type alias.
+- ValuePlug :
+  - Added Python bindings for derived classes' `ValueType` type alias.
+  - Added `now` argument to `clearHashCache()` method.
 - Color4fVectorDataPlug : Added a plug type for storing arrays of `Color4f`.
 - TypedObjectPlug : Added default value for `direction` and `defaultValue` constructor arguments.
 - VectorDataWidget : Added `setErrored()` and `getErrored()` methods to control an error state. Errors are reflected by a red background colour.
diff --git a/include/Gaffer/ValuePlug.h b/include/Gaffer/ValuePlug.h
index 80192d46eee..4913e88e953 100644
--- a/include/Gaffer/ValuePlug.h
+++ b/include/Gaffer/ValuePlug.h
@@ -185,9 +185,11 @@ class GAFFER_API ValuePlug : public Plug
 		/// Returns the total number of entries in both global and per-thread hash caches
 		static size_t hashCacheTotalUsage();
 		/// Clears the hash cache.
-		/// > Note : Clearing occurs on a per-thread basis as and when
-		/// > each thread next accesses the cache.
-		static void clearHashCache();
+		/// > Note : By default, clearing occurs on a per-thread basis as
+		/// > and when each thread next accesses its cache. Pass `now = true`
+		/// > to force all thread-local caches to be cleared immediately
+		/// > (this is not thread-safe with respect to concurrent computations).
+		static void clearHashCache( bool now = false );
 
 		/// The standard hash cache mode relies on correctly implemented
 		/// affects() methods to selectively clear the cache for dirtied
diff --git a/src/Gaffer/ValuePlug.cpp b/src/Gaffer/ValuePlug.cpp
index 3af7e9fb256..28d229c41c2 100644
--- a/src/Gaffer/ValuePlug.cpp
+++ b/src/Gaffer/ValuePlug.cpp
@@ -331,7 +331,7 @@ class ValuePlug::HashProcess : public Process
 			g_globalCache.setMaxCost( g_cacheSizeLimit );
 		}
 
-		static void clearCache()
+		static void clearCache( bool now = false )
 		{
 			g_globalCache.clear();
 			// It's not documented explicitly, but it is safe to iterate over an
@@ -341,11 +341,20 @@ class ValuePlug::HashProcess : public Process
 			tbb::enumerable_thread_specific<ThreadData>::iterator it, eIt;
 			for( it = g_threadData.begin(), eIt = g_threadData.end(); it != eIt; ++it )
 			{
-				// We can't clear the cache now, because it is most likely
-				// in use by the owning thread. Instead we set this flag to
-				// politely request that the thread clears the cache itself
-				// at its earliest convenience - in the HashProcess constructor.
-				it->clearCache.store( 1, std::memory_order_release );
+				if( now )
+				{
+					// Not thread-safe - caller is responsible for ensuring there
+					// are no concurrent computes.
+					it->cache.clear();
+				}
+				else
+				{
+					// We can't clear the cache now, because it is most likely
+					// in use by the owning thread. Instead we set this flag to
+					// politely request that the thread clears the cache itself
+					// at its earliest convenience - in the HashProcess constructor.
+					it->clearCache.store( 1, std::memory_order_release );
+				}
 			}
 		}
 
@@ -1239,9 +1248,9 @@ void ValuePlug::setHashCacheSizeLimit( size_t maxEntriesPerThread )
 	HashProcess::setCacheSizeLimit( maxEntriesPerThread );
 }
 
-void ValuePlug::clearHashCache()
+void ValuePlug::clearHashCache( bool now )
 {
-	HashProcess::clearCache();
+	HashProcess::clearCache( now );
 }
 
 size_t ValuePlug::hashCacheTotalUsage()
diff --git a/src/GafferModule/ValuePlugBinding.cpp b/src/GafferModule/ValuePlugBinding.cpp
index ed572f100dd..f3fdef36bea 100644
--- a/src/GafferModule/ValuePlugBinding.cpp
+++ b/src/GafferModule/ValuePlugBinding.cpp
@@ -139,7 +139,7 @@ void GafferModule::bindValuePlug()
 		.staticmethod( "setHashCacheSizeLimit" )
 		.def( "hashCacheTotalUsage", &ValuePlug::hashCacheTotalUsage )
 		.staticmethod( "hashCacheTotalUsage" )
-		.def( "clearHashCache", &ValuePlug::clearHashCache )
+		.def( "clearHashCache", &ValuePlug::clearHashCache, arg( "now" ) = false )
 		.staticmethod( "clearHashCache" )
 		.def( "getHashCacheMode", &ValuePlug::getHashCacheMode )
 		.staticmethod( "getHashCacheMode" )