Look at the flight tracker on flightaware.com. Their free data goes back about ten days or two weeks, much longer if you subscribe. You first look up the airline and flight number, then click on the list of dates to see details for your day, or just print out the list of dates which should show the cancellation.

Through the day after the flight, flight status on delta.dumb would do it.

Perhaps this is a reminder that we should all do this when one of our flights is cancelled, for instance if one's employer wants documentation for extra time and expenses or if ORC later becomes an issue because DL thinks the rerouting was voluntary.