[CentOS-virt] Getting guest to detect new drive without reboot

I've got a CentOS 5.6 guest running on 6.0 host.

Using virsh attach-disk, I attached a new raw file as vdc However, the guest does not detect this new disk.

In the past, I've used the following echo "0 0 0" > /sys/class/scsi_host/host#/scan

command to make a CentOS system scan for new drives.

However in the guest, there is no host in scsi_host so this isn't an option.

I can't seem to find any information on doing this any other way apart from a reboot. Does anybody know if there is any other way?