I have done it several times from USA this H1-B Extension beyond 3 years using following criteria: you don't need to go back home unless you want to stamp visa on your passport(Visa revalidation which also can be done i n mexico or canada if you have approved h1 copy)

1) Labor certification must be filed 365 days before the current H-1 Expiration date and is either pending or approved.  I
  You will get 1 yr extension
Or
2) I-140 must be approved and current visa bulletin must be unavailable to file I-485(doesnot matter when you file your labor certification in this case)
  You will get 3 yr extension
hope this helps!