public void empty(final Iterable<Key> keys) {
		final Map<Key, Object> updates = new HashMap<>();

		for (final Key key: keys)
			if (cacheControl.isCacheable(key))
				updates.put(key, null);

		this.memcacheWithRetry.putAll(updates);
	}
public void empty ( final Iterable < Key > keys ) { final Map < Key , Object > updates = new HashMap < > ( ) ; for ( final Key key : keys ) if ( cacheControl . isCacheable ( key ) ) updates . put ( key , null ) ; this . memcacheWithRetry . putAll ( updates ) ; }
Revert a set of keys to the empty state.  Will loop on this several times just in case
the memcache write fails - we don't want to leave the cache in a nasty state.