Caches in PI

I have a situation where there are application servers that are not configured for load balancing, so the individual hostnames show up in the rwb workbench and under administration - data caches with the direct name. If an application server goes down, the cache refresh links won't work if they are pointing to a server that is down.

Where do you do a refresh to change the URL to an existing server? I'm looking at <hostname>:50<nr>0:/dir and then administration and data caches. I see entries for like "af.<application server hostname>. Where do I refresh to put that to a functional host?