Disk caching probably invokes Flava Works vs Gunter [1] which is a case that distinguishes streaming from copying under copyright law. There are probably later updates to this, but this is the one I'm aware of.
Leave it to the copyright people to make a huge legal mess out of the simplest concepts. Now people can't even cache data without lawyers showing up. I wonder how long it's gonna take before I see them arguing memcpy should be illegal.