You may try what happens with Redis server-side Set intersections. This could help in theory, at least if you have a way to sort the output data (that will be unsorted).
Basically you need a lot of RAM, and to put in keys called something like "tag:<tagid>" all the IDs of your products having such an ID.
Then if you want all the products IDs having as tags both foo, and bar, you ask Redis the following: SINTER tag:10 tag:20
Using SINTERSTORE is also possible to put the result into a new key, and then use SORT to sort this data.
Basically you need a lot of RAM, and to put in keys called something like "tag:<tagid>" all the IDs of your products having such an ID.
Then if you want all the products IDs having as tags both foo, and bar, you ask Redis the following: SINTER tag:10 tag:20
Using SINTERSTORE is also possible to put the result into a new key, and then use SORT to sort this data.