This method Removes local role assignments and inherits role assignments from the parent object.

If a list has some items that are using unique permission you can reset the permissions back to list using this method.

SPListItem.ResetRoleInheritance();

Thanks to the SDK

mk:@MSITStore:C:\Program%20Files%20(x86)\Microsoft%20SDKs\SharePoint%202010\SP2010SDK.chm::/html/b814e6a6-8b27-5d27-e6c3-2fbc5fc1e284.htm