Remove OWA auto complete entries programmatically

We recently moved from Groupwise to Office 365. A major pain point during the migration was having invalid entries in the OWA auto complete cache. We finally came up with a powershell script that would go through and remove invalid entries.

Assuming you already have the Exchange and MSonline Powershell modules, the first thing you will need is the Microsoft Exchange Web Services Managed API 2.0 located here.
You also need to create an impersonation user in Exchange. Instructions can be found here.

After that you can use the script below with a few modifications for your organization. Use the script at your own risk. I can't ensure it will work or not break anything. I'm just sharing a solution that worked for us.