How can I reset a factory_girl sequence?

Just call FactoryGirl.reload in your before/after callback. This is defined in the FactoryGirl codebase as:

module FactoryGirl
  def self.reload
    self.factories.clear
    self.sequences.clear
    self.traits.clear
    self.find_definitions
  end
end

Calling FactoryGirl.sequences.clear is not sufficient for some reason. Doing a full reload might have some overhead, but when I tried with/without the callback, my tests took around 30 seconds to run either way. Therefore the overhead is not enough to impact my workflow.