Adobe has provided a mechanism by which one can prevent their machine from being tracked in this fashion: the Flash Player Settings Manager.
http://www.macromedia.com/support/do...s_manager.html
The Flash app on this page controls the global and per-site permissions for the storage of Shared Objects (i.e. the tracking cookies described above), access to your Microphone and Webcam, and more. The instructions provided for each "tab" are fairly straightforward and comprehensive but, to solve this particular issue:
Go to
http://www.macromedia.com/support/do...manager03.html
Drag the slider on this panel down to "None".
You will now be prompted whenever a site wants to store Flash data. You can allow or deny that site, and optionally choose to never be asked again.
Go to
http://www.macromedia.com/support/do...manager07.html
If you want to eliminate ieSnare tracking only, select "mpsnare.iesnare.com" in the list and click "Delete website".
If you want to delete ALL Shared Objects from your system, click "Delete all sites". Note that plenty of Flash games and LEGITIMATE APPS store their save game progress or settings here, so you may be wiping out more than you intended.
As far as I'm aware, these settings govern both Flash content accessed in your browser AND Flash content embedded in desktop apps like the poker clients. It's fantastic to have this degree of granular control over the data stored on your machine by Flash Player. Unfortunately, Adobe has done a piss-poor job of exposing its existence to the end user.