Yeah, this is confusing.
Each of the configurations you listed creates it's own JGroups channel, so in reality you have 4 'partitions'. Each needs its own channel, because multiple services sharing the same channel doesn't work well. The major goal of the upcoming JGroups 2.3 release is to make it possible for multiple services to share the same channel. With that available, the default behavior in JBoss AS 5.x will be for the services you listed to share a channel, thus allowing a single 'partition'.
For the 3 tree caches, suggest you change their config file to include something like this:
You can then set the value of the system property jboss.partition.name and the name of your 'logical partition' will be picked up by each of the channels.
To set the system property:
run.sh -g MyPartition (4.0.3 and later)