Filter showing empty attribute values

Hi,

On the provided page the filter is displaying filter values for all products in the shop. How can we make it so the filter only displays attribute values of the products that are shown on this page? For example the brand (merk) FOSS has no dumbbells, but the brand value is still shown in the filter. Also the price filter shows the maximum price of the most expensive product in our shop, even if the product is not shown on the page.

The page I need help with: [log in to see the link]