This is a very tough question for numerous reasons. Naturally if you daughter had told you about this over the course of the (7 years) it allegedly took place it would be a "no brainer" to confront your husband.
You stated it was only (after) you made it clear that you did not want her back into your life that she revealed these allegations to you and she also refused to provide you additional details.
I believe you are going to have to trust your gut instincts on this one. Do you believe your daughter is capable of being so vindictive as to want to destroy your marriage of 20 years or do you believe you married to a child molester. You've painted a picture of your daughter which includes ample ammunition for why she is not the most reliable person in the world but you did not say anything about your observations of your husband.
The fact that you're even asking the question is an indication that on some level you believe there is a "chance" your daughter might be telling the truth. If you thought your daughter was without a doubt a vile liar you would have dismissed her comments immediately as another attempt to manipulate you.
If you don't believe your daughter and have no plans to be a part of her life you can act like you never heard this and continue to living your life. One thing is for certain if you broach the subject with your husband it will forever change your marriage.
You might offer to go into therapy sessions with your daughter.
If she refuses to do it then maybe it was all a lie to hurt you. If she really wants to be in your life she'll say "yes" just to have the opportunity to spend time with you at the very least. And if she does say yes maybe during your sessions together you'll uncover the truth about the alleged incidents or at the very least develop a mutual understanding of how you hurt one another over the years which led to the current state of your relationship. Best wishes!