at 6 stacks procs onhit abilitys 2x as it reads. What about items like 
and 
That being said if it does, I'd like to take the question slightly deeper. What if a 
used his Purge (w) or espically in the OP case of 
could he infact using his clone. Proc duskblade's passive on hit effect 4tims? Also in the case of Would it drain mana for both times it was proc'd or more than once during Urgot's Purge?
TheFallenShaw1 votesGuess no one knows the answer, or just never thought about procing a duskblade 4 times. Sad really people used to be good at finding the next op builds, esp since ginsuews doesnt require champions to charge.
Shuyin1781 votesIt can't proct Duskblade itself because it's a consumed on-hit effect. If it was a sustained one like Manamune or Ruin King then it would go off twice, but because it gets consumed on first use you can't proct it twice. It's just like if you were using Rageblade on say Nasus, you can't proc his Q damage twice because it gets consumed on use. Finally, yes it does take Manamune's mana twice.
Here is the list of everything Rageblade works with http://leagueoflegends.wikia.com/wiki/Guinsoo%27s_Rageblade#On-Hit