when you do a release on a texture object, when the context is destroyed, when the glDeleteTextures is called.. you just have to enumerate it all, but eventually all functions are passed to the graphic drivers to be translated into gpu operations.
It's as same as saying that a HDD driver can zero deleted files and delete temporary files when a process is killed because it translates API calls into HDD controller commands.
Yes, the idea is that the manufacturer is in the position of knowing the most efficient way to talk to it's gpu and the driver knows everything it's happening memory wise. It'd be interesting to have a prototype done in some open source linux driver. Tbh, I'm probably not good enough for that.