GTM deployment

ltms im ok w/ question is if I am going to run a gtm in a backup data center w/ it's own ltms and a primary data center w/ its own ltms in reading the docs (and I know this is a loaded question) but I was thinking the gtm's would exchange data and each datacenters gtm would query the ltm local to it and pass that data on (am I wrong in this thinking?)

 

 

one deployment guide led me to believe that you code both gtms to query not only it's local ltms but the other data centers ltm's as well.

 

 

so im kinda stuck at the moment- I want both gtm's to be live and answer internet queries but the backup data center will not have much running in it unless we are in a DR scenerio.