Following an emergency failover, and there is a risk of the transaction sets differing between parts of the ClusterSet, you have to fence the cluster either from write traffic or all traffic. Even though you primarily use fencing on clusters belonging to a clusterset, it is also possible to fence standalone clusters from all traffic.
From MySQL Shell 8.0.28, three fencing operations are available:
<Cluster>.fenceWrites(): Stops write traffic to a primary cluster of a ClusterSet.
<Cluster>.unfenceWrites(): Resumes write traffic.
<Cluster>.fenceAllTraffic(): Fences a cluster from all traffic.
For more details, see Section 8.9.1, “Fencing Clusters in an InnoDB ClusterSet”.