There seems to be some confusion among one or more PGP about the compensation for unfair detention process in Italy. No one - not even Raffaele Sollecito - claiming compensation for unfair detention in Italy need be concerned about Illinois or Wisconsin laws, nor UK (neither England/Wales nor Scotland nor NI) laws. By the way, as far as I have been able to find, Wisconsin does not have a statute relating to a "certificate of innocence" while Illinois does have such a statute.
According to Merriam-Webster (online), quash means "to suppress or extinguish summarily and completely". Source: https://www.merriam-webster.com/dictionary/quash
The legal definition of quash: Quash means to nullify, void or declare invalid. The procedure is used in both criminal and civil cases when there is an irregularity or defect in procedures. ... Source: https://definitions.uslegal.com/q/quash/
Now, regarding the likely next step in Sollecito's claim for compensation for unfair detention, his lawyer was quoted as stating she will take the case to the ECHR. Compensation for arrest and/or detention which violates the requirements listed in Convention Article 5 as determined by the ECHR (for example, in its existing case law) is required under the European Convention of Human Rights, Article 5.5, as well as Italian Constitution Article 24 and CPP Article 314. A quick search for such cases in HUDOC shows a listing of 226 ECHR judgments. Assuming that Sollecito and his lawyer(s) submit an application to the ECHR claiming that Italy violated his Convention rights by unfairly denying him compensation (likely to be complaints of violations of Article 5 and Article 6), it will be the eventual judgment of the ECHR that will determine Italy's actions according to international law (Italy's treaty obligations).
Sollecito's potential case against Italy for a violation of his Convention rights for the denial of compensation for unfair detention (under Convention Articles 5 and 6) would in all probability not be judged until after Knox v. Italy 76577/13 was final. Since the “reasoning” for Sollecito's arrest and detention and for the denial of compensation to Sollecito was based in part on the false allegations that were made against Amanda Knox, an ECHR judgment in her favor would likely be helpful to his case. A judgment in her favor is highly likely, based on ECHR case law.