VXLAN is prepared across a specific datacenter ... if you want to stretch the VXLAN isolation across multiple, it's possible: Scalable Cloud Networking with Cisco Nexus 1000V Series Switches
I'm not sure if you need to have a Nexus or comparable network hardware ... it was just one example.
also, when you say datacenter, do you mean different physical locations ... or same location ... just a different 'datacenter' in vCenter?