Guernsey Cream is an early large flowering hybrid so a pruning group 2 clematis. These bloom primarily on growth that was formed the previous season so recommendations are to prune lightly in late winter or early spring, removing the uppermost growth down to a plump set of viable buds. Once they have finished their initial early bloom, you can repeat this process to encourage a late summer or early fall rebloom.

Many avid clematis growers ignore these instructions in favor of a harder pruning, simplifying the process into a 2 group pruning method - prune or not prune :-) Sometimes they are helped by winter cold, which will take the vine down back to its root system. Others - like myself with too any clematis to fuss with - give them a hard prune like recommended for group 3 vines. All that does is push back the initial bloom flush by a few weeks.

Given your zone 4 location, I'd suspect winter will do a pruning for you. You will just need to cut back and clean up the dead stuff that winter leaves behind.

Thank you. I need to edit my location, sorry. No longer in northern Michigan. I'm in SE Michigan now.