Hi Anil,
Try the following depending on whether it is power or ground:
addNet -physical vddcore
addNet -physical gndcore
setNet -net vddcore -type special
setNet -net gndcore -type special
dbSetIsNetPwr vddcore
dbSetIsNetGnd gndcore
More info is in solution:
http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNumber=11732912
Thanks,
Brian