Is it possible to manage the iCloud keychain?
As described in Apples iCloud FAQ: To delete the Keychain completely, you have to deselect Allow approving using security code in the iCloud Account details under system preferences. After that, turn off the Keychain usage on every device that is using it. This will delete the complete keychain. Turning on the Allow approving using security code will result in a clean keychain.

If you want to edit items stored in the iCloud keychain you can do so via the Mac OS X keychain app or from your iDevice in the Safari preferences.

Mac OS X example: On the left, select iCloud and delete / edit items on the right.