Linux NFS - 'stat' on defunct NFS mount causes blocked ('D') state processes and high load average

I'm rearranging some NFS mounts - tidying up and decommissioning them.

As part of this, my 'management' server has gained a huge load average, because of nagios kicking off 'stat' on the NFS mounts.

All the processes have gone into state D - uninterruptible sleep.

Is there a way - short of rebooting the box - that I can convince these processes that the mount they're accessing is dead and gone? I know they're irrelevant, but the kernel masks interrupts to these processes.