Don't you need the interface to be defined in the common module? I guess I misunderstood.

I think a fair chunk of it could be extracted. What does a JMS/JGroups backend basically need? Access to a Serializer and_Deserializer_, right? Everything else should be transparent and could go into a separate module.

You could take this to the extreme and argue that the remote backends could also go into their own modules. Not sure how useful that would be.