Offline cache files are located in a hidden %SystemRoot%\CSC folder. You should not touch these files manually though.
To re-initiate offline files cache in Windows XP
Open Windows Explorer > Tools > Folder Options > Offline Files > hold CTRL + SHILT and press Delete Files.
Above unfortunately doesn’t work in Windows 7.
In Windows 7 you can re-initiate offline cache via a small registry change.
Open regedit.exe and navigate to
Create new DWORD type entry: