Master-Master replication between two PXC clusters

How to achieve conflict resolution in Master-Master replication between two 3 node PXC clusters? Since wsrep_auto_increment_control=ON does not honor setting auto-increment-increment and auto-increment-offset, are there any other options to differentiate the data originating in each of the clusters other than to capture some local cluster identifier in each transaction like hostname:timestamp or something like that?