Hi Bobby,
I hope I'm not missing something easier but how about you create a custom checkbox field in SFDC ("Synced Marketo <--> SFDC") on the lead & Contact object, at the next sync those two fields should be created as one field in Maketo. Then run a batch campaign on all your leads in Marketo where SFDC type is not empty AND SFDC is deleted = false, Flow change data value of "Synced Marketo <--> SFDC" to true.
This will give you everyone that is in sync at the moment the campaign is run. You would then need to create a series of trigger campaigns to manage the updates the newly synced leads.
Trigger Lead is synced to SFDC - Flow Flow change data value to true
Trigger: Lead is created source is saleforce.com - Flow change data value to true
Trigger: Data value changes SFDC Is deleted (New value = true) - Flow change data value to true
The only scenario I don't think it can cover is if a lead is in sync between the two, the checkbox is set to true and then you delete the lead in Marketo only leaving it in SFDC, because the lead has been deleted in Marketo there's no way for Marketo to push info to that SFDC lead any more. One option might be to create a delete campaign and the flow would be change data value to false, Sync lead to SFDC, wait 1 minute, Delete in Marketo only.
Of course remember that as soon as that lead/contact gets updated again in SFDC it will sync back down to Marketo (assuming the Marketo sync user can still see the lead in SFDC).
Hope that helps.
Rgs,
Cathal
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