Question on MSTP regions.

Hi.

Is the MSTI information of one region present in the MST BPDUs of another region?

Here I have two Regions, each with several MSTIs.

EX1----EX2------------EX3----EX4

Region A                         Region B

I understand that the BPDU between EX1 and EX2 has information on all of Region A's MSTIs. 

Does EX2's BPDU over the CST to EX3 contain information on all of Region A's MSTIs?

        If not, how does EX2 know to remove it.

        If yes, does EX3's BPDU to EX4 contain info on Regions A's MSTIs along with Region B's? If not, how does EX3 know to remove it?

Thanks,

Deepak