Dear @All Terrain Expedition Camper Trucks,
Thank you for posting your question in the Microsoft Q&A forum.Based on your description, you have already cleared the Outlook contact suggestions cache and waited 48 hours, but the contacts still appear, you wonder can this be cleared manually via the admin center.
Outlook contact suggestions are generated from multiple sources (AutoComplete cache, mailbox data, contacts, and Microsoft Search). Clearing the cache removes the current list, but it is automatically rebuilt, which is why the same contacts can reappear. There is currently no option in the Microsoft 365 Admin Center to manually clear a user’s AutoComplete or suggestion cache. These settings are managed at the user/mailbox level. If the issue persists, you may need to remove entries individually, check contacts/suggested contacts, and clear browser or client cache as applicable.
In the meantime, I sincerely recommend you go to Feedback community to vote your feedback via Ideas · Community. The product team is in charge of the site, and they constantly check customer reviews and feedback. The higher votes, the more attention the related team will pay on. And a lot of the features are developed and improved based on customer feedback.
Additionally, you can refer to this article: How to Hide Users from Global Address List (GAL) - o365info (Please note that this method only works for contacts linked to the Global Address List (GAL), not for personal contacts.)
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If you have any other questions, please feel free to reach out. I'm glad to support you again.