If i attack with Victarion's Reavers and the losing player just have the location of House of Dreams, he still have to discart the location?

Claim, even replaced claim like with the Reavers ot Pyat Pree, is not a card effect. So the "non-plot card" immunity granted by House of Dreams cannot protect the location in the scenario you suggest. The Reavers work on the claim, then the claim works on the location.