Eh, Mike's post was a bit misleading. Basically, think of it this way:
Your Spell Progression is EXACTLY the same as if you remained a Cleric. You still get your Domain slots, you still get your Domain spells, all that's fine.
The associated power, however, is usually dependant on your Cleric level. For example, if you had the Strength Domain, its Domain Power grants you a +1 enhancement bonus to Strength per level of Cleric you have. So if you were a 10th-level Cleric/5th-level Loremaster, the Strength Domain would only give you a +10, even though you're 15th level for purposes of Domain spells. This also applies to abilities like the Smite from the Destruction Domain, or the Turn/Rebuke powers of the Elemental Domains. Some Domain powers, however, like the +1 caster level of the Healing, Good, Evil, Law, and Chaos Domains, aren't based on level and therefore still grant the benefit if you take a Prestige Class.