How can I correct a group's count of available items?>

[Colin Baxter]

I have a group called "nnml:mail.expiry" which is set to the value of
the variable nnmail-expiry-target. I am then able to expiry mail items
to nnml:mail.copy as an intermediary before final expiry. (The expiry
target is set to delete as a group property in nnml:mail.expiry.)

All works well, except I am told that there a couple of hundred
available items in nnml:mail.expiry whereas the actual number is only
7. The group nnml:mail.expiry was formed by renaming an existing group,
using gnus-group-rename-group, and I suspect this somehow corrupted the
item count.

How can I correct the count of the number of items in nnml:mail.expiry?

Thank you.

Colin Baxter.