Given a subscribed calendar with a url like
https://example.com/example.ics
To force Google Calendar to refresh and reload the contents right now, unsubscribe from the calendar and subscribe to a new calendar with a URL like
https://example.com/example.ics#1
Adding the anchor tag will force Google Calendar to think of it as a new calendar
Many people who come to this gist are not looking for a one time forced refresh but instead to refresh recurringly. If that's you, you should check out @derekantrican 's Google App Script
https://github.com/derekantrican/GAS-ICS-Sync
Which can refresh a calendar automatically every N minutes
Thanks to @rattrayalex for pointing people to this script
Got one more, despite "var addAlerts = "yes"; ", the alerts are not coming over into the GCal. Am I missing something, I've tested various methods and reminder times.