default_scopeはunscopedで外す。

with_exclusive_scope (ActiveRecord::Base) – APIdock

In Rails3 use "unscoped" instead

The with_exclusive_scope examples no longer work in Rails3 because with_exclusive_scope is now a protected method which can and should not be used in a controller. Use the new unscoped method instead:

ほー。

class Post < ActiveRecord::Base
  default_scope :published => true
end

Post.all #=> SELECT * FROM posts WHERE published = true

Post.unscoped.all #=> SELECT * FROM posts

ほほー。