How do I expire home page cache when an article is updated?

I'm attempting to use a sweeper to clear the home page index action when a new article is published.

The home page cache is working fine in development environment and expires after 1 minute. However when an article is saved, the sweeper action is not triggered.

class HomeController < ApplicationController
  caches_action :index, :expires_in => 1.minute
  cache_sweeper :article_sweeper
  def index
    @articles = Article.published.limit(5)
  end
end

class ArticleSweeper < ActionController::Caching::Sweeper
  observe Article
  def after_update(article)
    expire_action(:controller => 'home', :action => 'index')
  end
end

Either I've gone wrong somewhere or a different approach is needed to expire the home page cache.

My app uses ActiveAdmin to update articles, and Dalli for Memcache (as I'll be using Heroku).

Two steps to the solution:

The controller performing the changes on the model needs to have the sweeper reference, not the destination controller as shown above. In this case it is active_admin, so I added this to my admin/articles.rb file (source) instead of the home controller.

controller do
  cache_sweeper :article_sweeper
end

And the controller name needs a slash

expire_action(:controller => '/home', :action => 'index')