Using RSS feeds to follow couponing blogs - How do I clean my subscriptions up?

I searched all over the place for an answer to this, and there may be a better place to ask but I don't know what it would be.

I have a huge list of 40+ couponing/deals sites I follow in my RSS reader. As you can imagine, the same coupons/deals get posted multiple times per hour, day, etc ... Is there any way to maybe plug my subscriptions into an online tool and see which blogs are only posting duplicate content that I have already seen once so I can unsubscribe from them? Obviously I could keep up with this manually but it would be very time consuming and I hate knowing I could mess it up somehow and miss out on any killer deals in the future.

Here's my list of subscriptions if it helps:

Addicted To Saving

All Things Target

Common Sense With Money

Coupon Cravings

Coupon Mom

Couponers United

Coupons

Cuckoo For Coupon Deals

Daily Cheapskate

Deal Seeking Mom

DealCatcher

Fabulessly Frugal

FatWallet

For The Mommas

Free Tastes Good

Frugal Coupon Living

Hip2Save

I Heart Kroger

I Heart The Mart

Ibotta Rebates

Kroger Krazy

Living Rich With Coupons

Mojo Savings

Money Saving Mom

My Frugal Adventures

MyLitter

Passion For Savings

Penny Pinchin' Mom

Saving With Shellie

Slickdeals

Southern Savers

Spoofee Deals

Stretching A Buck

The Coupon Project

The Krazy Coupon Lady

Totally Target

Wild For CVS

Wild For Wags