how to clear cache in SharePoint [on hold]

How do I clear cache for a AD distribution group? I recently had a change in outgoing smtp via central admin. I have a workflow that sends email to a distribution group which has been working great. all after the smtp change distribution group is being routed to another distribution group by SharePoint. Is there a way to clear cache so that it doesn't do that. Messaging team emailed me the log showing how sharepoint re-routing to a another distribution group.