> [...] data warehouses are built for this very reason. [...] [cache invalidation and denormalization] are largely solved problems [...]

Uhm, no. Data warehouse is not a database with operational (i.e. current) data, it's a database with historical data. If it is out of sync with production for a day or a week, it's totally OK, depending on its design.

So no, cache invalidation is not a solved problem there.