The Cloud in a Cloud in a Cloud

I was meeting with some IS Directors a month or so ago and they asked:

How do I better understand how all these "cloud" offerings interact with each other?

So, assuming that you use the cloud for storage, but you use another cloud service for a specific application and have all this served to a VDI client....That's alot of movement in the cloud. I understand his concern for the security of this data, but also the importance that these partners work together.

I would think that strengthens the cloud vision that host all cloud services out of the same DC. I believe you can clearly have different clouds for unrelated things like conferencing with Webex where you host the service and it clearly does not interact with many other parts/pieces, but what about the clouds within a large cloud. All this has my head in the clouds.