Web App and Cache Problems

We have a website that I recently updated. The changes to the website are 
seen at every location except for on the client's network (go figure). It 
seems as though they are seeing an old page without the current changes.

The client has tried to access the website from PCs that have and have not 
connected to the website before. I have attempted to clear the cache on the 
user's PC using internet options and the following commands:

ipconfig /flushdns
net stop dnscache
net start dnscache
ipconfig /release
ipconfig /renew

None of this has worked. We are now thinking that the PCs are accessing a 
network cache in order to display the page (since both PCs that have and 
have not connected to the website before are displaying an old page). What 
is the best way to clear a network cache?

Based upon your description, it seems more than likely that your client has a
caching proxy server on their network that is keeping an old copy locally to
speed up requests.  There are several of these on the market and each is a
little different.  You probably want to get with the client's network
administrator and see if perhaps the proxy server's cache can be reset.