environment.rb

if defined?(PhusionPassenger)
  PhusionPassenger.on_event(:starting_worker_process) do |forked|
    if forked
      # Rails cache_store
      Rails.cache.instance_variable_get(:@data).reset if Rails.cache.class == ActiveSupport::Cache::MemCacheStore

      # Reset the session_store, value could be nil depending on how you set it up
      ActionController::Base.session_options[:cache].reset

      # Reset the cache_fu connection (if used)
      CACHE.reset if defined?(CACHE)
    end
  end
end