Massive spike in percentile memory graph

Hi

I've got a host that has apparently sent false info to the hobbit server,
and the result is that the monthly graph shows a flatline with a "80M %"
memory use.
I don't want to delete the whole rrd file, is there any way to truncate this
graph to only show below 101% usage?

I'm using hobbit 4.2.0 on a Centos 5 linux server, and the same version
hobbit client on a solaris 9 client

Thanks
Stefan