Do you know that when you delete cookies stored inside your computer, it is not necessary that all the cookies information is deleted. There are some websites that set cookies by Flash. And it can’t be deleted using traditional method.
Important Note: You might know about Incognito mode in Google Chrome where any data (browsing history, cookies) can’t be stored. But it is not always true. As you can’t disable plugins in the private mode, there are chances that Flash might store the data about sites you access in this mode.
To watch the cookies stored in Flash, you can visit Abobe Settings Manager page. It will show you all the websites that are using Flash to store cookies on your PC.
According to Adobe
In this panel, you can change storage settings for a website or delete the website so that, if you visit it again, it will use your global settings instead of any individual settings you may have set. You can also delete all sites, which erases any information that may have already been stored on your computer.

How to delete individual cookies
To delete the individual cookie, click on the name of website in the box given. Now click on the “Delete website” button.

A pop up will appear, click on the “confirm” button.

How to delete all the cookies
To delete all the cookies information, click on the “Delete all sites” button.

A pop up appears. Click on “Confirm” button to delete all the cookies information stored inside your computer by the websites.

All done. All the cookies information is deleted. You can visit the Adobe setting manager page to delete the cookies time to time.
How to prohibit websites from storing any information
Go to Global Storage Settings panel. Now set the slider at left most position. It will assure that Adobe will get no disk space to store the information on your computer.

Also uncheck the box next to “Allow third party Flash content to store data on your computer”.
Note: According to Adobe: If you prohibit websites from storing information, the website might or might not function as intended.