How to fully reload an ActiveRecord to reset it's memoized values?

The good way is the one you already have: Completely recreating the object.

You cannot "reload" the object's memoized values in any easy "Rails" way, as memoizing attributes isn't a function of Rails or ActiveRecord. Neither knows anything about how you're memoizing methods.

You can do that by redefining reload. For example if you memoized with ||= you can do that:

class Foo < ActiveRecord::Base
  def bar
    @bar ||= rand
  end

  def reload
    @bar = nil
    super
  end
end

For ways to reset all instance variables see Is there a clean API for resetting instance variables on 'reload' in ActiveRecord?

If you use the memoist gem you can call flush_cache there.