1. No Need To Wipe Dalvik Cache After Reflashing
2.Go To Clockwork Mod Recovery And Then Goto Advance There You CAn See The Option Wipe Dalvik Cache Click It And Select Yes..
3. Download The StockRom From SamMobile Firmware Page ..... And Flash It Using Odin ..
4.If You Are Upgrading It Is Not Necessary..If Not Then You Can Tick Re-Partition..