You have mastered the subtle intricacies of the divine power you’ve devoted yourself to.
Prerequisite: Access to relevant domain.
Benefit: You can cast spells associated with one of your domains at +1 caster level. This benefit also applies to caster level checks to overcome a target’s spell resistance as well as other variables such as spell duration. If you cast a spell from one of your nondomain spell slots, this feat does not help you, even if the spell also happens to appear on your domain list.
Special: You can take Domain Focus multiple times. Its effects do not stack. Each time you take the feat, it applies to a new domain to which you have access.
Source: Complete Divine, page 80.