Dumb ideas are circulating, so here's mine:
The Federal Reserve puts out a news release stating that a small but still considerable amount of US currency was printed with contaminated ink. The contaminated ink contains a chemical that is proven to be carcinogenic. The contaminated ink has been discovered in samples dating back to 1994 right up to the present day.
It is too difficult to recall individual series of currency since the contamination problem was across the board. Therefore, the Fed will issue new currency to replace all older currency printed before 2010. This older currency will become worthless in 30 days, which is plenty of time to go to your bank and exchange your old contaminated paper money. Few of us have more than a hundred bucks in cash laying around at any given time, so it's no big deal. But it needs to be done relatively quickly due to public health concerns and public safety.
The drug tycoons in Central and South America and militant islamicists in Afghanistan and Pakistan would be up a creek because they'd have to spend the money before it became worthless. The re-patriated money would create an orgy of domestic spending in the US, assuming they could smuggle the money back into the US before the expiration date. Even better, they couldn't use their dollars to buy more drugs and weapons back home because their suppliers won't take money that will be worthless very soon.
So it's a dumb idea, but central bankers are capable of dumber.