Marketo Sync Behavior: Unchanged Field ‘bulkupdate’ Persisting as TRUE in AEP

Hi Team,
We have a business requirement where, whenever bulk data is ingested in Marketo, the records should flow to AEP with the attribute bulkupdate = true. Subsequently, for any genuine (normal) updates to the same records, the bulkupdate flag should be reset to false, and the updated data should flow to AEP accordingly in the same flow run.

However, based on our testing, we are observing that bulkupdate = false is only being set when specific attributes are updated. Since it is not feasible to include all attributes in a Smart Campaign trigger, this approach is not scalable.

Could you please advise:

Which attribute or trigger should be used to reliably identify any genuine update to a record?
Is there a recommended approach in Marketo to handle this type of logic, where a field needs to behave like a reset flag after any update?

For example, we attempted to use Updated At as a trigger, but it is not qualifying records as expected.

Looking forward to your guidance on the best-practice approach for this scenario.