Sometimes you do indeed need to start over with a soak (sometimes a simmer) and a scrub. Don't forget to condition it afterwards (heat up, food grade oil with a rag or paper towel until it shines and is dry), and be kind to it until it redevelops it's water repellent surface. Getting it out to treat it even if you aren't cooking with it regularly.
I use my Grandma's Chicken Fryer (dutch oven) and trust me, It's been soaked, cooked with acidic foods, and scrubbed with steel wool more than once in the last 100 years. Need to get new handle though for her old knife, it's getting thin but still maintains an amazing edge.