In our setup, we have a loadbalancer that redirects to web1 and web2. Clearing the cache results in clearing either web1 or web2, depending on the load balancer...
Ich server has its own cache in /var/nginx/cache/TYPO3.
I do not know what happens, if we define a path that is shared over the server? may be it works. but if not, defining endpoints for the cache purge call would be great. So both paths could be cleared...