Collaboration Process Diagrams - do I need to maintain second process in two places?

[philip_kisloff]

I'm trying to get collaboration diagrams to work, and am struggling to "bring in" a second process which is communicated to by a message. Surely, I don't have to maintain this second process in a second process diagram? However, not sure what the correct method is (if there is one!)

For example, with a collaboration diagram with one process defined, I added a second pool and linked it to the second process.

And I want to end up something like this below, but here I feel I cheated and simply re-drew the second in the colloboration diagram of process Anvil. Not only is that going to be a problem with complex second processes, but it means maintaining one process in two places.

Is my approach wrong? What am I missing?