Accusative is used for motion toward.
Domum means to the house/home. It needs no preposition, just as, in English, you can say I'm going home : there is no need to say "I'm going to home" (although that isn't "wrong").
This abbreviated form (lacking the usual preposition) is found in several languages (perhaps because of the frequency of expressing "homeward") e.g. English I'm going home, Russian Я иду домой, Croatian Idem kući.