In the past there was a cmdlet Refresh-LibraryShare that would allow you to refresh the library cache for an SCVMM server.
It no longer exists in the current VirtualMachineManager module.
I can see from this list: IT from my perspective: Virtual Machine Manager: Changes from 2008 R2 to 2012 Beta 1 (LONG) when it was removed, with nothing to replace it.
Does anyone know how to perform a library refresh using the current SCVMM module? (or any other way?)