Must Have The Domain Selected
I am basing my answer on the text in the Cleric's SRD:
Deity, Domains, and Domain Spells
A cleric’s deity influences his alignment, what magic he can perform, his values, and how others see him. A cleric chooses two domains from among those belonging to his deity. A cleric can select an alignment domain (Chaos, Evil, Good, or Law) only if his alignment matches that domain.
If a cleric is not devoted to a particular deity, he still selects two domains to represent his spiritual inclinations and abilities. The restriction on alignment domains still applies.
Each domain gives the cleric access to a domain spell at each spell level he can cast, from 1st on up, as well as a granted power. The cleric gets the granted powers of both the domains selected.
With access to two domain spells at a given spell level, a cleric prepares one or the other each day in his domain spell slot. If a domain spell is not on the cleric spell list, a cleric can prepare it only in his domain spell slot.
And I am expanding further from Page 53 of Complete Champion:
Clerics and Domain Feats: If you are a cleric (or any other character class who gains access to a domain), you can choose any domain feat corresponding to the list of domains offered by your deity, even if you do not have access to those particular domains. A cleric of Pelor, for example, can choose to cast spells from the Good and Healing domains but select the Strength Devotion and Sun Devotion feats.
In addition, you can choose to give up access to a domain in exchange for the corresponding domain feat. Doing so allows you to select up to three domain feats, but you cannot prepare domain spells or use the granted power of the sacrificed domain. In essence, you trade in a domain for an extra feat slot that you can spend only on a specific domain feat. For example, the above cleric of Pelor could choose to give up the granted power and spells of the Good domain for the Good Devotion feat.
Availability vs. Access
Having an availability is not the same thing as having access. The White House is available to the public. But that doesn't mean the public has access to the President's Oval Office. Regarding Domain Feats, you can't give up access to a domain that isn't selected. So if I never took the Law Domain, I can't trade that out for a bonus feat; because I don't access to it yet. I only have it available.
Available Domains for Pelor: Glory, Good, Healing, Strength, Sun
At 1st I will have access to two domains out of the 5 available.