The wiki currently suggests simply "building=yes" with "telecom=data_center". (I would prefer to have something like "building=telecom", but that would be for another time.)

I personally believe OSM items should be self-explanatory, so that, eg, it is reasonably easy to locate "data center buildings" via Overpass Turbo. If we go for "avoid duplicated tags" then it would be difficult to locate buildings inside data center land uses (search "telecom=data_center" -> for each area find buildings within polygon -> for each building reject if is non-generic building).