My point is that what you’re asking for isn’t “domain knowledge” strictly speaking. Using an XOR to swap two variables w/o a temp variable is only really useful when memory is expensive (embedded programming, et al). If you’re not interviewing for an embedded programmer why are you worried about it?
Same with the modulo trick. The first time I ever encountered that I was writing a Perlin Noise Generator based off of someone else’s work. Outside of routines that need to be highly optimized there’s no reason for it.
Are you trying to hire an ASP.Net programmer or an embedded systems programmer? Granted, the XOR trick is pretty well known, but not knowing it off the top of your head says nothing about your abilities as a programmer (whereas the fizzbuzz example does).
No one can know everything. I would expect that type of attitude from a non-IT person, but not someone who is interviewing programmers.