I would say that you lose access to all domains, previous and those gained in other fashion later, like advancing in contemplative, unless they are from the hospitaler list of domains. If you have domains, two or more, switch out domains until you run out of them. Then you run out of luck. It does kind of suck for a cleric who is not into those domains, but the class gives you most of the paladins abilities, the ability to multiclass freely with a paladin, feats comparable to a fighter, AND a full complement of cleric spell levels. In a way, you could almost consider it a little over powered.