I think the response of aaron can be enhanced for URL that contains variables:
var sdk = require('postman-collection');
const testURL=pm.environment.values.substitute(pm.request.url, null, false);
const objURL=new sdk.Url(testURL);
console.log("clearing cookies for: "+testURL);
const jar = pm.cookies.jar();
jar.clear(objURL, function (error) {
// error - <Error>
if(error)
console.log("Error clearing cookies: "+error);
});