For those who need a quick solution for live event attendance tracking in lieu of the Marketo Events App, you can use a Smart Campaign. In the Smart List, identify the emails who have checked in. Then use the “Change Program Status” Flow Step to set their attendance to “Attended” for the specific event. If you want to go further, you can create a custom/branded Landing Page and a form to collect the emails with a script that clears munchkin cookie after submission. You can then run those collected emails through the Smart Campaign you created.
You want to remove the Munchkin cookie from the form data. No need to remove the cookie completely.