Manual:$wgSquidServersNoPurge/en

Details
This variable is about telling MediaWiki an array of  blocks where any IP address part of the range has to be considered as a Proxy server.

Same as, except that MW has no methods to send HTTP PURGE to an origin part of the configured ranges.

All documentation in Manual:$wgSquidServers#Configuration example with Varnish is valid, but with difference described below.