public void invalidate(String clusterName, String hostName) {
    Map<String, String> clusterMapping = m_hashes.get(hostName);
    if (null != clusterMapping) {
      clusterMapping.remove(clusterName);
    }
  }
Invalidates the cached hash for the specified agent host in the specified
cluster.

@param clusterName
         the name of the cluster (not {@code null}).
@param hostName
         the host to invalidate the cache for (not {@code null}).
ambari-server/src/main/java/org/apache/ambari/server/state/alert/AlertDefinitionHash.java