Well if we are to continue using the analogy with cells, then what happened after multicellularity was a type of fractioning (because multicellular species can't share genomes as fluidly as single celled species can). So in this analogy each noosphere would be its own "species" that interacted (on a weak to strong continuum) with other noospheres in a noosphere type space environment. The strength of the interactions would probably be dependent on their proximity, their ability to transfer information (interstellar internet?), and their evolutionary history.
Of course, it is possible that the analogy breaks down after Global Brain has been achieved. It could be that once we are a Global Brain we just keep expanding the sphere and remain one collective intelligence without fracturing into different noospheres. I'm unsure if there is anyway to test which future is more probable.