def serviced_by(token)
      if @cache[token]
        @cache[token] = Time.now.to_i
        @lru.push(@lru.delete(token))
        @identity
      end
    end
def serviced_by(token)
      if @cache[token]
        @cache[token] = Time.now.to_i
        @lru.push(@lru.delete(token))
        @identity
      end
    end
Determine whether request has already been serviced

 === Parameters
 token(String):: Generated message identifier

 === Return
 (String|nil):: Identity of agent that already serviced request, or nil if none