Not to speak of landuse=farmyard, which could with a bit of squinting be considered farmland. 
I just run a JOSM query "type:way closed nodes:50- (building=* | ( landuse=residential & areasize:-10000))" followed by a simplify, "building areasize:-3" and "delete". The most tedious part is downloading megabytes of nodes in tiny pieces because the server won't give you any more.