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
Turned out, if you run the script without editing the ICS link, the script crashes and self-destroys itself. After I recreated another copy and added the URL to calendar ICS , the error didn't appear again. Not very user-friendly, but it finally works. Thanks to the author!