Filters list should filter the filters

Or, put more correctly, the filters you select should filter the product search results (as it does already) but then, the products that you see in the search results should filter the filter categories as well as the filter attributes. I.e if you filter shoes to a given brand, say "Clarks" and clarks only do black and brown shoes, then the "blue shoes" filter option should disapear.

Also, the filter attributes should have a number next to them e.g. Black (5) that tells you there are 5 black shoes in the results. If you then filter by brand, again to say "Clarks" then this might change to Black (3) - because while there are 5 black shoes, there are only 3 black shoes after filtering the brand to Clarks.