Deleted Groups are visible in _layouts/groups.aspx

Hi,

I have a site collection which has around 30 groups created. These are visible when we navigate to sitecol/_layouts/user.aspx. I then deleted 15 groups using powershell (sitegroups.remove()). These disappeared from sitecol/_layouts/user.aspx, but surprisingly these were still present when i navigated to sitecol/_layouts/groups.aspx !

How do we ensure that the groups are deleted completely from the site collection?