It's been a while since I've been on 4.2.3 but I have in my notes to look in the JMX console under:
jboss.partition=mycluster,service=HAPartition -> Current View Property
Where "mycluster" is obviously the name of your cluster.
What you want to find is the jgroup's current "View". It will look like this:
[172.17.172.229:40879, 172.17.172.227:56257, 172.17.172.228:35004]
The first address in this list is the "master" with respect to that cluster. Cluster being the JGroups cluster, which is probably what you're after.