You specify which domain to use when you log in. There are a few special domains: "Global", "MDS", and "System Data". To add a host in the Global domain, you would do something like this:
mgmt_cli -f json -d "Global" -r true login > session.txt
mgmt_cli -f json -s session.txt add host name "test" ip-address "192.168.178.1"
mgmt_cli -f json -s session.txt publish
mgmt_cli -f json -s session.txt assign-global-assignment ...
mgmt_cli -f json -s session.txt logout
rm session.txt
The call to "assign-global-assignment" is needed to actually distribute the object from the Global domain to the CMAs. I'm not 100% sure how it should be called. If you're fine refreshing the global assignment from SmartConsole, you can leave that line out.