In Symfony Cache 3.2, we're going to ship tag based invalidation with TagAwareInterface and the tag() method on CacheItem, and namespace based invalidation with ForkableAdapterInterface in #19521.

See pending doc PR to know how they are intented to be used:
https://github.com/symfony/symfony-docs/pull/6858/files?short_path=2b6cef4#diff-2b6cef44ab8160dd54c3796627fbff0b

Symfony 3.2 will be released in 3 months. During that period, I'd be really happy to get feedback from implementers of PSR-6 to see if and how these interfaces could be promoted to a new PSR that they might be interested in implementing.

ping @Nyholm @aequasi @tedivm @andrerom