From the nfs(5) man page:
nosharecache
As of kernel 2.6.18, it is no longer possible to mount the same same filesystem with different mount options to a new mountpoint. It was deemed unsafe to do so, since cached data cannot be shared between the two mountpoints. In consequence, files or directories that were common to both mountpoint subtrees could often be seen to be out of sync following an update.
This option allows administrators to select the pre-2.6.18 behaviour, permitting the same filesystem to be mounted with different mount options.
Beware: Use of this option is not recommended unless you are certain that there are no hard links or subtrees of this mountpoint that are mounted elsewhere.