Perhaps you would be able to chose two domainsbut would have to chose which Domain Spells you would use..
Say for instance you had the Fire and Protection Domain
and you got ....
ya know what on second thought...
Say you have your two domains and instead of chosing when you rest or soemthing you have a certain number of uses of the individual tiers. Say you have Fire and Travel Domains and are a level 1 cleric
Instead of having to chose between the two tier one abilities during a rest you just have a pool of three uses to choose from,
So you could use 1 use of Expeditious Retreat and 2 uses of Burning Hands
Having 2 Domains however could mean that the power would need to be toned down a touch... though not necessarily