Ok i had similar questions, and i am trying to consolidate bits and pieces of info lying else where to get this thread moving ( and possibly this can serve as unofficial document)
Disclaimer : i have not attempted to set this up yet/ or tried these out 
At high level cross dc/xdc architecture look something like this post
So In my opinion one need to
a) setup two independent temporal clusters using existing helms
b)Enable global namespace in cluster metadata section
c) configure kafa for replication across the two clusters
Refer global domain registration and kafka replication for step B and C
d) of course needless to say all this got to be on TLS, some info on TLS setup is available in docs
e) the below tctl commands can come handy to viewing changing membership details
on a side note : Please be aware kafka will bring zookeeper dependency too.
@maxim, @ryland, @samar do you have additional pointers here?