To protect your privacy, all modern web browsers provide an option to delete browsing history and cookie data, but not all browsers are able to deal with data stored by plug-ins. For example, flash local storage objects (also known as flash cookies) cannot delete the same way as we delete browsing history and cookie.
So, even if you delete browsing history and usual cookie data from the browser, data stored by plug-ins (here it is flash cookies) can still open a way to track what you are doing online.
However, the latest version of Google Chrome (Dev channel, Canary, and Chromium builds) and Internet explorer (IE8/IE9) can delete flash cookies from with in the browsers. This was made possible by the NPAPI ClearSiteData, which Adobe has implemented in the latest build of Flash Player 10.3.
To enable this option in Google Chrome, go to Tools – Clear browsing data (Ctrl + Shift + Del) and check the checkbox near the middle of the dialog, which appears ‘Delete cookies and other site data and plug-in data’.
For Internet Explorer, Flash cookies will delete when you delete your normal cookies with ‘Delete Browsing History’ option. If you select this option, Flash Player will automatically clear your Flash cookies (more info here)
Note: For IE, this feature only works if you have installed latest Flash Player 10.3 (RC) and use it with IE8 or IE9.