I deploy my applications using a bash script that automates GitHub & Heroku push, database migration, application maintenance mode activation and cache clearing action.
In this script, the command to clear the cache is :
heroku run --app YOUR_APP_NAME rails runner -e production Rails.cache.clear
This works with Celadon Cedar with the Heroku Toolbelt package. I know this is not a Rake-based solution however it’s quite efficient.
Note : be sure you set the environment / -e option of the runner command to production as it will be executed on the development one otherwise.
Edit : I have experienced issues with this command on Heroku since a few days (Rails 3.2.21). I did not have time to check the origin the issue but removing the -e production did the trick, so if the command does not succeed, please run this one instead :
heroku run --app YOUR_APP_NAME rails runner Rails.cache.clear