Make Selected Mutiselect Items "selected"

I’m developing a theme settings panel for a new wordpress theme that have an option to exclude categories from being shown in the loop. I managed to get the main functionality to work, using a mutilselect box and saving the values as array …

<?php $cats = get_categories('hide_empty=0&orderby=name'); ?>
<select name="<?php echo $option['id']; ?>[]" id="<?php echo $option['id']; ?>" multiple="multiple">  
    <option value="0">None (don't exclude anything)</option>
    <?php foreach ($cats as $cat_list ) { ?>
        <option value="<?php echo $cat_list->cat_ID; ?>" <?php selected( $selected, $cat_list->cat_ID ); ?>><?php echo $cat_list->cat_name; ?></option> 
    <?php } ?>
</select>

however I can’t understand how check every item in foreach() loop if its value matches one value in the stored values array, then apply selected="selected" if it returns true to it. I understand selected() wp function but don’t understand how to make use of it in this case ( multiple values inside foreach() loop ).

Any help will be appreciated, I’m a n00b so forgive me if it’s a stupid question 🙂