Exclude contacts from receiving other emails whilst in nurture program

if you're building out the nurture using a smart campaign and not an engagement program, you can add in flow steps to toggle marketing suspended - annoying but the easy solution

otherwise, have a global exclusion list controlled by a boolean that you absolutely include for everything and check it for those contacts in your special nurture program

Ok, so to ensure they don't get any other content while they are in the engagement program you probably want to build membership of that engagement program as a filter in all other sends. Hopefully this isn't too complicated but this wouldn't require any extra fields in Marketo or workarounds. 

Another thing you could do is build a campaign status in SFDC, and use that as a filter instead for all other sends. Eg. campaign status is "Nurture", then build out that filter in each send you have. 

There aren't many options that I can think of that will "automatically" exclude someone from all other sends. And it's probably best not to. Ongoing, if this sort of situation will happen often, you could set up a segmentation or some sort of structure to it so it's built into your workflows. For example, we have five different "engagement levels" for our leads, and they are mutually exclusive. Each one corresponds with an engagement program. So you can't get content from more than one at once. The logic is built into our structure.

There's not a way in Marketo to put them in a "swim lane" where they only get nurture emails. The best thing to do is to build in a filter in all your program templates so that any email sent has the filter

Member of engagment program is false

program is any

cadence is normal