The manual page flock(2) had been out of date for a long time, but has since been updated to say (emphasis mine):
Since Linux 2.6.12, NFS clients support flock()
locks by emulating them as byte-range locks on the entire file. This
means that fcntl(2) and flock() locks do interact with one another
over NFS.
Since Linux 2.6.37, the kernel supports a compatibility
mode that allows flock() locks (and also fcntl(2) byte region locks)
to be treated as local; see the discussion of the local_lock option
in nfs(5).
That is from the official man-pages web site, http://man7.org/linux/man-pages/man2/flock.2.html which shows the new version from man-pages 4.00
Linux 2.6.12 was released in 2005.
This was originally meant to be a comment on janneb’s answer, but I didn’t have the reputation at the time. The doc update happened in 2014: http://git.kernel.org/cgit/docs/man-pages/man-pages.git/commit/man2/flock.2?id=e449654fdb3f19aafc569df47d12bffdf6276236