according to that technet article it is possible to reset manually the content index.
I was wondering if that task could be plan to run once a week for instance, automatically?
I could find no OOB way to do this in stsadm or PowerShell, so you could either write a server specific custom timer job that does this at pre-scheduled interval, or create a PowerShell cmdlet that is called using schedule on the server that runs the Search Service Application.
Alternatively in PowerShell
Corey Roth also coded this functionality as a cmdlet in his SharePoint PowerShell Community Toolkit
didn't try, but you can try in powershell:
then you can schedule the powershell command