Topology updates are sent while holding the ClusterCacheStatus lock, so they should never block. However, when MFC is present, the topology update can block waiting for enough credits. As most CacheTopologyControlCommands need to acquire the ClusterCacheStatus lock, this can easily lead to a full remote-executor pool (and OOB pool) and the appearance of a deadlock.
What's more, if one node is not responsive, it can block all the other nodes from receiving further topology updates. Topology updates should be as prompt as possible, so we should use the NO_FC flag to ensure that each node receives topology updates as soon as possible.