How to remove a set of custom object records from the Salesforce Campaign object

We use Eloqua integrated with Salesforce.com via the Salesforce integration app. Salesforce Campaign members are stored in a custom object. I mention this because this is the only Eloqua instance I've used to date and I don't know if there are other methods that could be in use.

The problem I am trying to solve is that when contacts in Salesforce.com are removed from a Salesforce campaign, they remain in the Eloqua custom object as associated with that campaign. I.e., a segment with the filter "Has Linked Contact in Custom Object"->Campaign Name = to "ABC" will still show people who are no longer in the campaign.