No you can't really and, even if you could, it still doesn't seem scalable. I would suggest you go about this a slightly diff. way: instead of knowing how many servers there are and how to reach each one, instead just have a single Azure Service Bus Topic. Then, part of the startup logic for your web application goes out and subscribes to this Topic. Next, when it's time to clear something, you send a single message to the Topic. That message will then be fanned out to each subscriber (web app instance that's listening) which, in turn, will take care of clearing the specified cache entry from its local cache.
The contents of the message will depend on your caching scheme, but I imagine all that it needs to contain is the key of the cached item you want to force the refresh of.