Chivalry would be easier for me to visualize. Space is actually such a broad concept that it's hard for me to envision just how the Domain affects the Power. Since you're considering Chivalry, I'll scrap the Quests idea, and that could almost be a Secondary Domain of Chivalry. Plus I wasn't too invested in Quests anyway.
I'm actually leaning toward the Power of the Forgotten. Seems to mesh well with Diadora's writeup, and it's a domain that would be very easy to use, plus give some interesting potential conflicts with the Excrucicans. A concept that's Excruciated is not just forgotten, it never was, however it could be argued that excruciation is just a small step up from forgetting. If noone remembers does it really matter that it existed?