@Subscribe
  public void invalidateCommandCacheOnHostRemove(HostsRemovedEvent event) {
    LOG.info("Invalidating HRC cache after receiveing {}", event);
    hostRoleCommandCache.invalidateAll();
  }
Invalidate cached HostRoleCommands if a host is deleted.
@param event @HostRemovedEvent
ambari-server/src/main/java/org/apache/ambari/server/actionmanager/ActionDBAccessorImpl.java