Do they mean naturalized citizens or natural born citizens?
There is no such thing as a domestic citizen.
A Domestic citizen would be a citizen who lives and is in the US, including territories.
A non-Domestic US citizen would be a citizen who lives outside the US. That could be:
Military assignment
Missionary, aid worker
Business man
Retiree
traveler, vacationer
Birth baby who went back to China
A Domestic citizen would be a citizen who lives and is in the US, including territories.
A non-Domestic US citizen would be a citizen who lives outside the US. That could be:
Military assignment
Missionary, aid worker
Business man
Retiree
traveler, vacationer
Birth baby who went back to China