Varnish in front of multiple servers with versioning

I've got Varnish in front of multiple webservers, I can run them as native to varnish or through upstream checks via nginx, but only static content is cached (no surprise), also respecting query strings i.e.

/main.css?v=1 and /main.css?=v2 are cached separately

I update servers one by one, in fact, all this cannot be done at exactly the same time without downtime, general deployment thing.

If main.css gets updated on one backend and I send request according to the new webpage version to the varnish and request /main.css?=v2, it may still look for file on the machine which has old version and where main.css hasn't been updated yet, so, now I am getting v1 in the cache as v2 and there is nothing I can do, unless TTL expires (which is too late).

I can manually invalidate cache via requests, that's ok.

Is there any automated solution without manual interfering on rewriting software for feedback to varnish? like:

1. Is it possible, to expire cache when backend comes up, after probe is good?
2. anything else?

Thanks