That kind of temperature isn't caused by dust. A few questions. How long have you had the card; did you receive it in this condition or has it just started to heat like that?
Make sure that the fan on the card is operating at all times. Sometimes a catalyst update will cause strange things to happen like fan problems and the such. If it isn't you may try setting it to manual fan control in the catalyst control center.
If that did not help give me some more information before I continue.