@Override
  public void invalidate(Object key) throws TimeoutException, EntryNotFoundException {
    invalidate(key, null);
  }
@param key the key to find
@param aCallbackArgument argument for callbacks
@param generateCallbacks whether callbacks should be invoked
@param clientEvent client-side event, if any (used to pass back version information)
@return the value associated with the key
geode-core/src/main/java/org/apache/geode/internal/cache/AbstractRegion.java